A motor control system for controlling a brushless motor controls the motor according to a rotational position of the motor detected by a sensor. A sensor signal output from the sensor contains noise or chattering, and therefore, a filter is used to remove the chattering and the noise. A rotational position signal representing the rotational position of the motor is generated according to the output signal of the filter, and a motor drive signal for driving the motor is generated based on this rotational position signal.
As described above, since the filter is used, the rotational position signal is delayed from a time at which the rotational position signal should be generated. For this reason, signal processing for generating the motor drive signal starts with the delay.
However, when a large noise occurs that cannot be removed by the filter, this noise is included in the motor drive signal. This may cause an abnormal current to flow through the motor and may cause the motor to abnormally rotate, thereby disturbing smooth rotation of the motor.
On the other hand, when a filter capable of removing a large noise is used, the delay of the rotational position signal further increases, which makes it difficult to perform the signal processing according to the rotation of the motor. In particular, when the rotational speed of the motor is high, the signal processing fails to catch up, and this may disturb smooth rotation of the motor.